(SPACE.com) -- Sitting on the hill of an alien world millions of miles from home, a hardy NASA robot celebrates an anniversary Monday -- one year on the planet Mars.

The Mars rover Spirit has come a long way since it hurtled down through the planet's atmosphere and came to a bouncy, airbag-protected stop at Gusev Crater on January 3, 2004.

It has survived more than four times its initial 90-day mission, driven miles across the Martian landscape and weathered a red planet winter only to scale hills for its human handlers.

A live webcast of NASA's One Year on Mars celebration begins Monday at 1:00 p.m. ET. NASA will commemorate Spirit's first year with a full day of programming, news conferences and even a rover birthday cake on NASA TV also beginning at 1:00 p.m. ET (1800 GMT) today.

Spirit continues to return data from the Columbia Hills, a region more than two miles (3.2 kilometers) from its Gusev Crater landing site. Scouring those hills has given Spirit -- and researchers -- more evidence that water shaped Mars' past.

Meanwhile, on the other side of Mars at Meridiani Planum, Spirit's robotic twin Opportunity is studying its own heat shield while it seeks to dig up more details on the area's watery past.

"It's astonishing to me how well it's going," said Steve Squyres, principal investigator for the Mars Exploration Rover (MER) project from Cornell University, of the mission in a telephone interview. "They're tough machines built by a fantastic team."

A software problem dogged Spirit in the early weeks of its mission when it fell silent for a period, but engineers were able to work through the glitch and resume the rover's science mission.

"That was waiting to bite us," Squyres said of the glitch, which involved Spirit's flash memory and required updated software to fix. "If Opportunity had landed first, it would have had the same problem."

Spirit has experienced other quirks, such as a finicky wheel that has left it dependent on only five of its six wheels to rove about Mars. But the glitch has not prevented rover from slowly making its way up "Husband Hill" in the Columbia Hills toward a vantage that researchers hope will give it a glimpse into a nearby valley.

"Spirit is our tough, hardworking robot," Squyres said, adding the rover is scratched and dusty. "Opportunity looks like she just came off the showroom floor, clean and pretty."

Squyres and other mission team members have become so adept at handling Spirit and Opportunity from Earth, they no longer need to congregate at NASA's Jet Propulsion Laboratory (JPL) to plan each moment of each rover's day. Instead, telephone and video conferences allow researchers to operate the rovers remotely.

"From an engineering standpoint, you really have to tip your hat," JPL's Matt Golombek told SPACE.com. "These rovers were designed for a lifetime of three months and now it's not clear when they're going to stop."